High voltage semiconductor devices are described herein. An exemplary semiconductor device includes a substrate, a first doped region disposed in the substrate and doped with a first doping polarity, and a second doped region disposed in the substrate and horizontally outside the first doped region. The second doped region is doped with a second doping polarity opposite to the first doping polarity. The semiconductor device further includes a third doped region disposed completely within the first doped region. The third doped region is doped with the second doping polarity. The semiconductor device further includes a first isolation structure disposed over the first doped region and spaced apart from the second doped region and the third doped region, a second isolation structure disposed over the first doped region and the third doped region, and a resistor disposed over the first isolation structure.