Abstract: A field effect semiconductor laser has two clad layers and an active layer therebetween, formed by an epitaxial growth on a semiconductor substrate, which is mesa-etched to form a stripe-shaped mesa part of a double heterostructure on the semiconductor substrate. The laser further includes first and second buried layers of conductivity types opposite to each other and formed on both sides of the mesa-etched part, respectively. Gate electrodes G are formed on at least one of the top faces of the buried layers, and a drain electrode D is formed on the mesa-etched double heterostructure part. Depletion layers are produced at the junction interfaces between the first and the second buried layers when a reverse-bias voltage is applied across pairs of these buried layers.