We demonstrate longitudinal beam-steering with a 1×16 silicon optical phased array (OPA) using a monochromatic light source and thermo-optic control of the refractive index in the grating radiator region. The refractive index is controlled by forming a series of n-i-n heaters, placing i-regions in each radiator of the OPA. When the biased voltage in the heaters is increased, the refractive index of the radiator region is increased by the thermo-optic effect, and the longitudinal radiation angle is changed according to the Bragg condition. The transversal beam-steering is accomplished by phase control with the phase shifters, which are devised with a p-i-n diode using the electro-optic effect. With these electro-optic p-i-n phase shifters and n-i-n thermo-optic radiators, we achieve a relatively wide 2D beam-steering in a range of 10.0°/45.4° in the longitudinal/transversal directions with a 1.55 μm light source. The tuning efficiency is 0.016°/mW in the longitudinal beam-steering.