We have used multi-step surface passivation process integrating electrochemical reduction and W exposure with native sulfidization by H2S gas to obtain high quality ZnS/p-HgCdTe interface. It shows very low parasitic interface charge density of the order of 10(10)cm(-2). The insulating ZnS layer also exhibits very high resistivity of similar to 10(12) Ohm cm. The resulting fabricated HgCdTe-MISFETs show 2D quantum effects. magnetoresistance measured at 1.5K displays oscillations which begin to appear above the gate voltage of 10V. They are identified as the Shubnikov-de Haas oscillations involving three electronic subbands.The magnetotransport data are quantitatively analyzed with the calculated Landau level-fan diagram and confirm the 2D subband quantization of the inversion layer at the ZnS/p-HgCdTe interface. This result demonstrates successful role of the multi-step surface passivation for realizing 2D ZnS/HgCdTe interface which will provide high quality 2DEG resevoir basis in future Hg-based narrow-gap nanostructure device applications.