This letter presents a wavelength-selective switch (WSS) based on a polarization-independent transmission grating and a high fill-factor micromirror array. The WSS does not require additional polarization management devices and successfully achieves a low polarization-dependent loss (PDL). A 1 × 4 port WSS has been successfully demonstrated. The maximum driving voltage is about 155 V and an applied overvoltage also illustrates the good reliability of WSS. The test results show that the PDL is less than 0.4 dB. The measured fiber-to-fiber insertion loss (IL) is in range from about 6 to 7 dB and the switching time is about 530 μs .