Pentax K-3 has a 24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Prime III processor. You can shoot at maximum resolution of 6016 x 4000 pixels with aspect ratios of and 3:2. K-3 has a native ISO range of 100 - 51200 and it can save files in RAW format which gives you a wider room for post processing.
Pentax K-3 is not the highest resolution APS-C camera. Canon M6 MII with its 33.0MP sensor is leading in this class. Check the comparison of Pentax K-3 vs Canon M6 MII or take a look at Highest resolution DSLR cameras list.
Pentax K-3 DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. Pentax K-3 sensor has been tested by DxO Mark and got an overall score of 80 for its image quality. You can find the details of their analysis of Pentax K-3 here.
Another important feature about Pentax K-3's sensor is the lack of anti-alias (Low-pass) filter. Removing anti-aliasing filter increases the sharpness and level of detail but on the other side it also increases the chance of moire occurring in certain scenes. But wait! K-3 takes care of this problem for you. It has a unique and adjustable Anti-Aliasing Filter Simulator mode which can create the effects of a Low Pass filter electronically when you want to avoid moire.
Let's look at how the size of the Pentax K-3's APS-C sensor compares with other standard sensor sizes.