A semiconductor device can include a substrate with a first source/drain and a second source/drain in the substrate. A first ohmic contact pattern can be in an uppermost surface of the first source/drain, where the first ohmic contact pattern includes a first semiconductor alloyed with a first metal. A second ohmic contact pattern can be in an uppermost surface of the second source/drain, where the second ohmic contact pattern includes a second semiconductor that is different than the first semiconductor and is alloyed with a second metal that is different than the first metal.