A novel InGaAsP/InP buried-ridge waveguide laser diode structure is proposed and demonstrated for use as a single-mode laser. The lateral mode of the proposed device can be controlled by adjusting the composition and thickness of the InGaAsP layer grown over the active region. Stable single-mode operation without kinks or beam-steering is achieved successfully with lateral and transverse in the junction plane even for the device with the ridge width of 9 ${mu}m$ up to an injection current of 500 mA.