InGaAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) are fabricated by a thermal selective wet-oxidation confinement technique. Post-oxidation annealing in a nitrogen environment at high temperatures is then conducted to improve the performance of the oxide-confined InGaAs/GaAs VCSELs. The optimum post-oxidation annealing conditions are determined by changing the furnace temperature and annealing time. Compared with a unannealed laser device, the light output power increases by about 12%. An aging test is carried out to examine the reliability of the annealed oxide-confined VCSEL device. The temperature dependence of the lasing wavelength of the annealed oxide-confined VCSELs is also investigated.