Wavelength multiplexing (WMUX) channel transmission bandwidth should be sufficiently large to compensate for thermal drifts of the emitters at the transmitter side of the link all over their functional windows in terms of driving currents and operational temperature of the environment. As well as that, a nearly absolute thermal insensitiveness of the WMUX device performance itself has to be ensured across the link over the widest possible temperature range. In other terms, devices have to exhibit the smallest thermo-optic coefficient, in order to fulfill system specifications under any thermal condition applied to the optical link. In this paper, we present coarse wavelength division multiplexing (CWDM), echelle grating (EG) WMUX to operate in the O-band (1310 nm) designed accordingly to 4 x 20-nm-spaced standard and fabricated on 200-mm Silicon Nitride-on-Insulator (SiNOI). Taking advantage of PECVD SiN low thermooptic coefficient compared to crystalline silicon, thermally-insensitive demultiplexers can be obtained. The device show insertion losses as low as 1 dB, interchannel crosstalk averaging -25 dB, non-uniformity of 1.3 dB and a -1 dB and -3 dB bandwidths of nearly 10 nm and 13 nm, respectively. Such wide channel bandwidths allow the compensation of wavelength drifts due to the different thermal environments between the transmitter and the receiver as well as the detuning of emitters at the transmitter side of the link. The EG shows a quasi-absolute thermal insensitiveness in the temperature operation range from 20 °C up to 80 °C, highlighting the thermal robustness of such SiNOI EG devices. A thermally-dependent chromatic dispersion averaging less than 13 pm/K over different channels has been estimated, thus 6x times less than similar devices when realized on standard SOI.