Polarization of vertical-cavity surface-emitting lasers (VCSELs) grown on (001) GaAs substrate has been controlled by electro-optic birefringence. Birefringence was induced at the top distributed Bragg reflector by applying an electric field along the [001] direction. The cavity resonance of the polarized light along the [110] or [1 (1) over bar 0] direction shifted to shorter and longer wavelength, depending on the direction of the applied electric field. By varying the direction and strength of the electric field, we actively controlled the polarization of VCSELs. The dominant polarization mode occurred along the [110] direction for the negative electric field, and along the [1 (1) over bar 0] direction for the positive electric field. (C) 2000 American Institute of Physics. [S0003-6951(00)04207-8].