Scientific Complementary Metal-Oxide-Semiconductor (CMOS) detectors have developed quickly in recent years, owing to their low cost, high availability and some advantages over CCDs, such as high frame rate or typically lower readout noise. With the development of the first back-illuminated models, these sensors started to be used in astronomy, so it is worth studying their characteristics, advantages and weaknesses. In this paper, we present the results of the laboratory characterization of the IMX455M and IMX411 sensors, integrated into the QHY600 and QHY411 cameras respectively. These are large (36×24 and 54×40 mm) native 16-bit sensors with 3.76 𝜇m pixels sensitive in the optical range. Their quantum efficiency has been found to peak at 80% at 475 nm, 40% at 700 nm and 10% at 900 nm. Their linearity and photon transfer performance have been evaluated, as well as their dark behaviour. They showed a low dark current, but also the presence of warm pixels of about 0.024% in the QHY600 and 0.005% in the QHY411, which were proved to be stable and linear with exposure time. We have analysed in detail the effect of random telegraph noise, also called Salt & Pepper noise, one of the most important issues to be addressed with these two sensors, since it affects around 2% of the pixels in each exposure. Sky tests are also presented and the effect of this noise on astronomical images is discussed.