Data are presented characterizing threshold and transverse mode behavior of microcavity lasers, which use a half-wavelength cavity spacer layer surrounding a single quantum well active region. Selective conversion of AlAs into AlxOy is used to define lateral device dimensions of 2, 5, and 8 μm. Initial results demonstrate a continuous-wave room-temperature lasing threshold current of 97 μA for a 2 μm device and 220 μA for an 8 μm device. We show that lasing operation is influenced by the AlxOy located only 200 Å from the quantum well.© 1995 American Institute of Physics.