Abstract: A gate oxide layer for a high voltage transistor is formed using methods that avoid thinning in the corners of the gate oxide layer. A recess is formed in a silicon substrate. The exposed surfaces of the recess are thermally oxidized to form a thermal oxide layer of the gate oxide layer. A high temperature oxide layer of the gate oxide layer is then formed within the exposed surfaces of the recess by chemical vapor deposition. The combination of the thermal oxide layer and the high temperature oxide layer results in a gate oxide layer that does not exhibit the double hump phenomenon in the drain current vs. gate voltage curve. The high temperature oxide layer may include a rim that extends out of the recess.