A semiconductor device includes an active gate metal structure disposed over a substrate, the active gate metal structure having a first sidewall and a second sidewall opposite to each other. The semiconductor device includes a first source/drain region disposed adjacent the first sidewall of the active gate metal structure with a first lateral distance. The semiconductor device includes a second source/drain region disposed adjacent the second sidewall of the active gate metal structure with a second lateral distance, wherein the second lateral distance is substantially greater than the first lateral distance. The semiconductor device includes a resist protective oxide (RPO) comprising a first portion extending over a portion of a major surface of the substrate that is laterally located between the second sidewall and the second source/drain region, wherein the RPO has no portion extending over a top surface of the active gate metal structure.