In this paper, a six channel DWDM demultiplexer based on Two Dimensional Photonic Crystal (2D PC) design is proposed to split the 25GHz, 50GHz, and 100GHz channels in a single demultiplexer. The functional parameters of the demultiplexer such as, normalized output efficiency, Q factor, crosstalk and channel spacing are investigated for each channel. The demultiplexer consists of three hexagonal cavities, seven waveguides and a channel drop cavity. The proposed demultiplexer drops the narrow spectral linewidth with the idea of raising the number of rods between bus waveguide and drop waveguide. The operating wavelength range of the demultiplexer is ranging from 1550 nm–1560 nm. The demultiplexer provides high transmission efficiency, high Q factor, uniform spectral linewidth and uniform channel spacing to meet ITU-T G 694.1 DWDM standard. The size of the device is about 363.52 μm2, which is within the fabrication tolerance and highly desirable for Photonic Integrated Circuits (PICs). © 2021, Springer Nature B.V.