We report an air jet cooler made with additive manufacturing. The air jet cooler directs an impinging air jet directly onto electronic devices. The jet system was fabricated by a single manufacturing process using a resin-based three-dimensional printer, and monolithically integrates two nozzles, air delivery channel, flow distributor and mechanical fixtures within a volume of 80x80x80 mm3. To demonstrate the viability of the jet cooler, high power gallium nitride (GaN) transistors were cooled using air jets at up to 195 m/sec. With the air jet, a GaN transistor could dissipate heat flux up to 60 W/cm2, which was 7X larger than the maximum allowable heat flux under natural convection cooling. The air jet cooler is also capable of rapid switching of the cooling air. Direct impingement of air jet could reduce the GaN transistor temperature by ~70°C within 11 seconds. This work demonstrates the potential of additively manufactured air jet coolers as a compact thermal management scheme for high-power electronics. Since the geometry of the air jet coolers can be easily tailored to various shapes, the demonstrated concept can be applied for cooling a variety of electronics with different topologies and different layouts of hot spots.