In this study, we demonstrate a high-power continuous-wave (CW) Tm:YAP slab laser that is endpumped by laser diodes in a dual-end-pumped configuration. The laser delivers an output power of up to 341.6Wat 1.99 μm, corresponding to a slope efficiency of 49.4% and an optical-to-optical conversion efficiency of 41.6% with respect to the total incident pump power of 822 W. To our knowledge, this is the highest output power of a Tm:YAP laser. At an output power of 300 W, the beam quality factors M2 are measured to be 260 in the x direction and 4 in the y direction, respectively. In addition, the power instability at the highest output power is measured to be 0.73% for 30 min. Also, we theoretically analyze the temperature distribution within the Tm:YAP slab crystal by the simulation software COMSOL 5.0. [ABSTRACT FROM AUTHOR]