Work function control of metal transistor gates was implemented with Al–Ni alloys. In addition to obtaining conventional capacitance-voltage (C-V) measurements to evaluate the work function, we microscopically characterized the work function distribution through scanning Maxwell-stress microscopy (SMM). The C-V curves of the Al–Ni alloys that we investigated exhibited work functions approximately between those of Al and Ni. The SMM analysis revealed that an Al–Ni alloy fabricated by the interdiffusion of a Ni/Al stack had a significant nonuniformity of the work function. This nonuniformity correlated with degradation of the C-V characteristics for interdiffused Al–Ni alloys.