A method for fabricating Complementary Metal Oxide Semiconductor (CMOS) compatible contact layers in semiconductor devices is disclosed. In one embodiment, a nickel (Ni) layer is deposited on a p-type gallium nitride (GaN) layer of a GaN based structure. Further, the GaN based structure is thermally treated at a temperature range of 350° C. to 500° C. Furthermore, the Ni layer is removed using an etchant. Additionally, a CMOS compatible contact layer is deposited on the p-type GaN layer, upon removal of the Ni layer.