We report tapered-ridge mid-infrared (λ = 3.75 μm) interband cascade lasers emitting up to 403 mW of continuous wave output power at T = 25 °C, with beam quality characterized by M2 = 2.3. One index-guided tapered structure consisted of a single 4-mm-long section with ridge width varying linearly from 5 μm to 63 μm. Another device that combined a narrow ridge of uniform width with a tapered section produced slightly lower maximum output power and brightness.