Pentax K-3 III has a
26.0MP APS-C (23 x 15.5 mm ) sized CMOS sensor and features PRIME V processor. On the other hand, Leica SL has a
24.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Maestro II processor.
Another similarity between these two cameras is that both Leica SL and Pentax K-3 III sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the K-3 III and SL sensor size comparison.
As seen above, Leica SL has a 2.4x Larger sensor area than Pentax K-3 III. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.