We used metalorganic chemical vapor deposition to fabricate a planar‐embedded InGaAsP/InP heterostructure laser with a semi‐insulating InP current‐blocking layer. The laser exhibits cw operation with a low, 20 mA threshold current and a high external differential quantum efficiency of 40% at room temperature. Measurements have also shown a small‐signal frequency response of 10 GHz due to an extremely small parasitic capacitance of 3.5 pF.