Microwave spectroscopy revealed a non-metallic effective dielectric function of non- supported nanocrystal networks. This new result is in agreement with the size-induced metal-insulator transition (SIMIT) observed in isolated sub-μm conductors. Separating the particle contribution ε = ε1 + iε2 from the measured effective dielectric response leads to the conclusion that percolating networks of SIMIT particles are characterized by an enormous positive value of El and a conductivity σ ∼ ε2 much smaller than expected for metallic networks. Another non-metallic feature of the networks is the weak thermal influence on ε1 and ε2. All properties change sensitively with the filling factor f of the network. Their unusual dielectric properties make low- density nanocrystal networks candidates for applications e.g. as high permittivity capacitor materials or temperature-independent resistors.