An active-matrix planar-type cold electron emitter array for application to high-sensitivity image sensors have been developed. A 640times480 pixel active-matrix HEED (high-efficiency electron emission device) with 20times20 mum pixels was fabricated, and the emission current density of 1 A/cm2 has been obtained at an applied voltage of 23 V. Further studies toward the next generation image sensor with a high sensitivity are in progress