We developed a high-power amplified spontaneous emission (ASE)-free fast wavelength-switchable external cavity diode laser (ECDL) using a digital micromirror device (DMD) as the wavelength selector. Generally, with a conventional fast wavelength-switchable ECDL with a DMD, the output power is limited by the damage threshold of the DMD. However, with our ECDL, a high-power output was realized by optimizing the beam focus on the DMD. In addition, an ASE-free stable output was realized through the introduction of a ring cavity. As a result, we successfully developed a fast wavelength-switchable ECDL realizing a high-power ASE-free output of over 300 mW.