A VCSEL includes a substrate, a first semiconductor multilayer of a first
conductivity-type, an active layer, a second semiconductor multilayer of
a second conductivity-type, a contact layer, each of the layers stacked
on the substrate. The second semiconductor multilayer constitutes a
resonator together with the active layer and the first semiconductor
multilayer. A metal layer is formed on the contact layer. The metal layer
includes an opening portion that defines a region that emits laser light.
When oscillation wavelength of the laser light is .lamda., optical
thickness T of the contact layer and a top layer of the second
semiconductor multilayer that contacts with the contact layer is smaller
than .lamda./4.