AbstractA discrete, tunable photonic integrated laser is showcased for multiwavelength spectroscopy of CO₂, H₂S, and H₂O. The laser combines an AlGaInAsSb/GaSb type‐I quantum well‐reflective semiconductor optical amplifier with a Si₃N₄ photonic integrated circuit (PIC). Operating at room temperature, the laser emits at 2670.42, 2629.12, and 2594.27 nm, with mW‐level average powers. The PIC employs a novel approach for achieving switching between three distinct emission wavelengths by using two cascaded tunable Mach–Zehnder interferometers (MZIs) that are connected to three spiral‐shaped narrow‐band distributed Bragg reflectors (DBRs). Phase tuning the arms of the MZIs allows the laser emission wavelength to be switched between the DBRs, while the DBRs themselves offer fine‐tuning of the emission wavelength. This design enables a simpler tuning mechanism with fewer control variables compared to hybrid PIC‐based lasers using Vernier architectures or a combination of multiple semiconductor amplifiers. Low‐loss and broadband MZIs are achieved by employing two interconnected directional couplers, which utilize asymmetric waveguides in the coupling region to effectively control the phase. Besides achieving state‐of‐the‐art performance for Si₃N₄‐based integrated lasers at 2.6 µm wavelength region, the demonstrated performance of passive components, including MZIs and spiral DBRs, opens new possibilities for mid‐infrared PIC technology.