An interesting aspect of 2D materials is the change of their electronic structure with the reduction of thickness. Molybdenum and tungsten-based transition metal dichalcogenides form an important family of 2D materials, whose members show a thickness-dependent bandgap and strong light–matter interaction. In this work, the experimental determination of the complex refractive index of 1-, 2-, 3-layer thick MoS ₂ , MoSe ₂ , WS ₂ , and WSe ₂ in the range from 400 to 850 nm of the electromagnetic spectrum is reported by using microreflectance spectroscopy and combined with calculations based on the Fresnel equations. It is further provided a comparison with the bulk refractive index values reported in the literature and a discussion of the difference/similarity between our work and the monolayer refractive index available from the literature, finding that the results from different techniques are in good agreement.