It is desirable to increase the operating temperature of long wavelength lead‐chalcogenide diode lasers to simplify cooling system requirements. Recently, double heterostructure Pb1−xEuxSeyTe1−y diode lasers (grown by molecular beam epitaxy) operated up to 147 K cw (180 K pulsed). The output photon energy of these devices is linear with x in the wavelength range 6.6– 2.7 μm. The growth of single quantum well lead‐chalcogenide diode lasers is now reported for the first time. These devices had PbTe quantum wells with PbEuSeTe confinement layers. The width of the quantum wells, Lz, was varied from 300 to 250 Å. Strong quantum effects are observed for Lz ≲ 1200 Å because of the small carrier masses (me∼mh∼0.04mo ). The shift in laser emission energy is in approximate agreement with that calculated from a finite square well potential. At low temperatures (≲100 K), these lasers appear to operate on transitions between n=1 states in the conduction and valence bands at threshold. Transitions between the n=2 states require a higher current which decreases with increasing temperature until the laser switches to the n=2 transition at threshold. The threshold current then increases relatively slowly with temperature, yielding cw operation up to 174 K (at 4.41‐μm wavelength), and pulsed operation up to 241 K (at 4.01 μm). These are the highest operating temperatures ever reported for lead‐chalcogenide diode lasers, and increases their potential usefulness for spectroscopic applications and for long wavelength fiber optics communications.