diff --git a/cpp_to_py/common/db/Layer.h b/cpp_to_py/common/db/Layer.h
index 22bcad4..564a78c 100644
--- a/cpp_to_py/common/db/Layer.h
+++ b/cpp_to_py/common/db/Layer.h
@@ -39,7 +39,7 @@ class Layer {
 
 private:
     string _name = "";
-    //'r' for route or 'c' for cut
+    //'r' for route, 'c' for cut, 's' for MasterSlice(pwell, nwell)
     char _type = 'x';
 
     Layer* _below = nullptr;
@@ -79,6 +79,7 @@ public:
 
     bool isRouteLayer() const { return _type == 'r'; }
     bool isCutLayer() const { return _type == 'c'; }
+    bool isMasterSliceLayer() const { return _type == 's'; }
     Layer* getLayerBelow() const { return _below; }
     Layer* getLayerAbove() const { return _above; }
 
diff --git a/cpp_to_py/common/io/file_lefdef_db.cpp b/cpp_to_py/common/io/file_lefdef_db.cpp
index 8475b93..114e069 100644
--- a/cpp_to_py/common/io/file_lefdef_db.cpp
+++ b/cpp_to_py/common/io/file_lefdef_db.cpp
@@ -748,6 +748,9 @@ int readLefLayer(lefrCallbackType_e c, lefiLayer* leflayer, lefiUserData ud) {
             return 0;
         }
         type = 'c';
+    } else if (!strcmp(leflayer->type(), "MASTERSLICE")) {
+        logger.warning("Find MASTERSLICE layer %s.", name.c_str());
+        type = 's';
     } else {
         return 0;
     }
@@ -888,6 +891,8 @@ int readLefLayer(lefrCallbackType_e c, lefiLayer* leflayer, lefiUserData ud) {
                 }
             }
             return 0;
+        case 's':
+            return 0;
         default:
             return 0;
     }
diff --git a/cpp_to_py/gpugr/db/GRDatabase.cpp b/cpp_to_py/gpugr/db/GRDatabase.cpp
index 3bf178b..ae62631 100644
--- a/cpp_to_py/gpugr/db/GRDatabase.cpp
+++ b/cpp_to_py/gpugr/db/GRDatabase.cpp
@@ -330,7 +330,7 @@ void GRDatabase::addCellObs(std::vector<RectOnLayer>& allObs, db::Cell* cell) {
     int dy = ctype->originY() + cell->ly();
     // Macro Obs
     for (auto& e : ctype->obs()) {
-        if (e.layer.rIndex == 0) continue;  // ignore M1 OBS
+        if (e.layer.rIndex <= 0) continue;  // ignore M1 OBS and non-routing layer
         int lx = e.lx, ly = e.ly, hx = e.hx, hy = e.hy;
         switch (cellOrient) {
             case 2:  // S
@@ -355,7 +355,7 @@ void GRDatabase::addCellObs(std::vector<RectOnLayer>& allObs, db::Cell* cell) {
     // Pin Box
     for (auto pintype : ctype->pins) {
         for (auto& e : pintype->shapes) {
-            if (e.layer.rIndex == 0) continue;  // ignore M1 OBS
+            if (e.layer.rIndex <= 0) continue;  // ignore M1 OBS and non-routing layer
             int lx = e.lx, ly = e.ly, hx = e.hx, hy = e.hy;
             switch (cellOrient) {
                 case 2:  // S