This application includes methods for detecting single nucleotide polymorphisms (SNPs) in a sample using an electronically addressable microchip having a plurality of test sites. A sample nucleic acid is electronically biased, concentrated at, and immobilized to a test site on the microchip. A mixture comprising a first labeled probe and a second labeled probe is electronically hybridized to the sample nucleic acid to form first or second hybridized complexes. The first labeled probe is perfectly complementary to the first sample nucleic acid and the second labeled probe is complementary to the sample nucleic acid and contains a nucleotide that forms a mismatch with the nucleotide at the site of the polymorphism. The first or second hybridized complexes are detected by determining a signal intensity of the label of the first or second probe.