An optical phase shifter and a method of making the same are disclosed. The phase shifter includes a substrate, a p-doped electrode and an n-doped electrode on the substrate, a first doped semiconductor layer on the p-doped electrode or the n-doped electrode and in electrical contact with the other electrode, a second doped semiconductor layer on the first doped semiconductor layer, a first vertical region electrically connecting the second doped semiconductor layer with the one electrode, and a cladding layer on or over the second semiconductor layer, the first vertical region, and at least a first sidewall of each of the first and second semiconductor layers. The p-doped electrode and the n-doped electrode form a p-n junction at an interface therebetween. The first and second doped semiconductor layers have the same doping type as the other electrode and the one electrode, respectively.