diff --git a/apps/web/messages/en.json b/apps/web/messages/en.json
index 900564ca..ca447870 100644
--- a/apps/web/messages/en.json
+++ b/apps/web/messages/en.json
@@ -727,7 +727,13 @@
     "filterByStatus": "Filter by status",
     "entries": "entries",
     "empty": "No knowledge entries yet",
-    "emptyDescription": "Entries will be auto-extracted from incidents, or you can create them manually"
+    "emptyDescription": "Entries will be auto-extracted from incidents, or you can create them manually",
+    "semanticSearchPlaceholder": "Enter semantic search query...",
+    "semanticOn": "Semantic",
+    "semanticOff": "Semantic",
+    "switchToSemantic": "Switch to semantic search (pgvector)",
+    "switchToKeyword": "Switch to keyword search",
+    "semanticSearchHint": "Enter a query to search with AI vector similarity"
   },
   "monitoring": {
     "healthy": "Healthy",
diff --git a/apps/web/messages/zh-TW.json b/apps/web/messages/zh-TW.json
index 66ed3fc4..7a6e0a49 100644
--- a/apps/web/messages/zh-TW.json
+++ b/apps/web/messages/zh-TW.json
@@ -728,7 +728,13 @@
     "filterByStatus": "篩選狀態",
     "entries": "筆",
     "empty": "尚未建立任何知識條目",
-    "emptyDescription": "知識庫將自動從 Incident 中萃取案例，你也可以手動新增"
+    "emptyDescription": "知識庫將自動從 Incident 中萃取案例，你也可以手動新增",
+    "semanticSearchPlaceholder": "輸入語意搜尋查詢...",
+    "semanticOn": "語意",
+    "semanticOff": "語意",
+    "switchToSemantic": "切換至語意搜尋 (pgvector)",
+    "switchToKeyword": "切換至關鍵字搜尋",
+    "semanticSearchHint": "輸入查詢內容，使用 AI 向量搜尋相關知識"
   },
   "monitoring": {
     "healthy": "正常",
diff --git a/apps/web/src/app/[locale]/knowledge-base/page.tsx b/apps/web/src/app/[locale]/knowledge-base/page.tsx
index 758840f7..ab2b1c0c 100644
--- a/apps/web/src/app/[locale]/knowledge-base/page.tsx
+++ b/apps/web/src/app/[locale]/knowledge-base/page.tsx
@@ -17,7 +17,7 @@ import { useTranslations } from 'next-intl'
 import { cn } from '@/lib/utils'
 import {
   Search, BookOpen, FileText, Shield, Cpu,
-  Server, Eye, Bot, ChevronRight, Plus,
+  Server, Eye, Bot, ChevronRight, Plus, Sparkles,
 } from 'lucide-react'
 import ReactMarkdown from 'react-markdown'
 import remarkGfm from 'remark-gfm'
@@ -105,6 +105,9 @@ export default function KnowledgeBasePage({
   const [selectedCategory, setSelectedCategory] = useState<string | null>(null)
   const [selectedType, setSelectedType] = useState<string | null>(null)
   const [searchQuery, setSearchQuery] = useState('')
+  const [semanticMode, setSemanticMode] = useState(false)
+  const [semanticResults, setSemanticResults] = useState<(KnowledgeEntry & { score: number })[]>([])
+  const [semanticLoading, setSemanticLoading] = useState(false)
   const [selectedEntry, setSelectedEntry] = useState<KnowledgeEntry | null>(null)
 
   // KB-D: approve/archive state (2026-04-03 ogt)
@@ -135,8 +138,35 @@ export default function KnowledgeBasePage({
   }, [selectedCategory, selectedType, searchQuery])
 
   useEffect(() => {
-    fetchEntries()
-  }, [fetchEntries])
+    if (!semanticMode) fetchEntries()
+  }, [fetchEntries, semanticMode])
+
+  // KB Phase 2: 語意搜尋 (2026-04-04 Claude Code)
+  const fetchSemanticResults = useCallback(async (q: string) => {
+    if (!q.trim()) { setSemanticResults([]); return }
+    setSemanticLoading(true)
+    try {
+      const apiBase = process.env.NEXT_PUBLIC_API_URL ?? ''
+      const res = await fetch(`${apiBase}/api/v1/knowledge/semantic-search?q=${encodeURIComponent(q)}&limit=20`)
+      if (res.ok) {
+        const data = await res.json()
+        setSemanticResults(data)
+      }
+    } catch (err) {
+      console.error('Semantic search failed', err)
+    } finally {
+      setSemanticLoading(false)
+    }
+  }, [])
+
+  useEffect(() => {
+    if (semanticMode && searchQuery) {
+      const timer = setTimeout(() => fetchSemanticResults(searchQuery), 500)
+      return () => clearTimeout(timer)
+    } else if (semanticMode && !searchQuery) {
+      setSemanticResults([])
+    }
+  }, [semanticMode, searchQuery, fetchSemanticResults])
 
   // KB-D: Approve / Archive handlers (2026-04-03 ogt)
   const handleApprove = useCallback(async () => {
@@ -235,16 +265,39 @@ export default function KnowledgeBasePage({
 
           {/* 頂部搜尋 + 篩選 */}
           <div className="flex items-center gap-3 px-4 py-3 border-b border-nothing-gray-200/50">
-            {/* Search */}
-            <div className="relative flex-1 max-w-md">
-              <Search className="absolute left-2.5 top-1/2 -translate-y-1/2 w-4 h-4 text-muted" />
-              <input
-                type="text"
-                value={searchQuery}
-                onChange={(e) => setSearchQuery(e.target.value)}
-                placeholder={t('searchPlaceholder')}
-                className="w-full pl-8 pr-3 py-1.5 text-sm font-body bg-nothing-gray-50 border border-nothing-gray-200 rounded-md focus:outline-none focus:border-claw-blue/50 transition-colors"
-              />
+            {/* Search + Semantic Toggle */}
+            <div className="flex items-center gap-2 flex-1 max-w-lg">
+              <div className="relative flex-1">
+                {semanticMode
+                  ? <Sparkles className="absolute left-2.5 top-1/2 -translate-y-1/2 w-4 h-4 text-claw-blue" />
+                  : <Search className="absolute left-2.5 top-1/2 -translate-y-1/2 w-4 h-4 text-muted" />
+                }
+                <input
+                  type="text"
+                  value={searchQuery}
+                  onChange={(e) => setSearchQuery(e.target.value)}
+                  placeholder={semanticMode ? t('semanticSearchPlaceholder') : t('searchPlaceholder')}
+                  className={cn(
+                    "w-full pl-8 pr-3 py-1.5 text-sm font-body bg-nothing-gray-50 border rounded-md focus:outline-none transition-colors",
+                    semanticMode
+                      ? "border-claw-blue/50 focus:border-claw-blue"
+                      : "border-nothing-gray-200 focus:border-claw-blue/50"
+                  )}
+                />
+              </div>
+              <button
+                onClick={() => { setSemanticMode(m => !m); setSearchQuery('') }}
+                title={semanticMode ? t('switchToKeyword') : t('switchToSemantic')}
+                className={cn(
+                  "flex items-center gap-1.5 px-2.5 py-1.5 text-xs font-label rounded-md border transition-colors shrink-0",
+                  semanticMode
+                    ? "bg-claw-blue text-white border-claw-blue"
+                    : "bg-nothing-gray-50 text-secondary border-nothing-gray-200 hover:border-claw-blue/50"
+                )}
+              >
+                <Sparkles className="w-3 h-3" />
+                {semanticMode ? t('semanticOn') : t('semanticOff')}
+              </button>
             </div>
 
             {/* Type filter */}
@@ -273,11 +326,21 @@ export default function KnowledgeBasePage({
 
           {/* 結果列表 */}
           <div className="flex-1 overflow-y-auto">
-            {loading ? (
+            {(semanticMode ? semanticLoading : loading) ? (
               <div className="flex items-center justify-center h-40">
                 <span className="text-sm text-muted font-body">{tCommon('loading')}</span>
               </div>
-            ) : entries.length === 0 ? (
+            ) : semanticMode && !searchQuery ? (
+              <div className="flex flex-col items-center justify-center h-60 gap-2">
+                <Sparkles className="w-10 h-10 text-claw-blue/30" />
+                <p className="text-sm text-secondary font-body">{t('semanticSearchHint')}</p>
+              </div>
+            ) : semanticMode && semanticResults.length === 0 ? (
+              <div className="flex flex-col items-center justify-center h-60 gap-2">
+                <BookOpen className="w-10 h-10 text-nothing-gray-300" />
+                <p className="text-sm text-secondary font-body">{t('empty')}</p>
+              </div>
+            ) : !semanticMode && entries.length === 0 ? (
               <div className="flex flex-col items-center justify-center h-60 gap-2">
                 <BookOpen className="w-10 h-10 text-nothing-gray-300" />
                 <p className="text-sm text-secondary font-body">{t('empty')}</p>
@@ -285,7 +348,7 @@ export default function KnowledgeBasePage({
               </div>
             ) : (
               <div className="divide-y divide-nothing-gray-100">
-                {entries.map(entry => (
+                {(semanticMode ? semanticResults : entries).map(entry => (
                   <button
                     key={entry.id}
                     onClick={() => setSelectedEntry(entry)}
@@ -336,12 +399,19 @@ export default function KnowledgeBasePage({
                         )}
                       </div>
 
-                      {/* Right: view count + chevron */}
+                      {/* Right: similarity score (semantic) or view count + chevron */}
                       <div className="flex items-center gap-2 flex-shrink-0">
-                        <div className="flex items-center gap-1 text-xs text-muted">
-                          <Eye className="w-3 h-3" />
-                          <span>{entry.view_count}</span>
-                        </div>
+                        {semanticMode && 'score' in entry ? (
+                          <div className="flex items-center gap-1 text-xs text-claw-blue font-label">
+                            <Sparkles className="w-3 h-3" />
+                            <span>{Math.round((entry as { score: number }).score * 100)}%</span>
+                          </div>
+                        ) : (
+                          <div className="flex items-center gap-1 text-xs text-muted">
+                            <Eye className="w-3 h-3" />
+                            <span>{entry.view_count}</span>
+                          </div>
+                        )}
                         <ChevronRight className="w-4 h-4 text-nothing-gray-300" />
                       </div>
                     </div>