The existence of a special type of resonances in the visible transmission spectrum of a very thin two-dimensional photonic crystal slab is demonstrated. We illustrate a controlling mechanism that allows the stabilization of the field amplification in a thin layer lattice with low contrast dielectric. Numerical simulations show that an extremely large field enhancement, as large as 700 times the amplitude of the incident wave, connected with high Q-factor resonances can be axcited. The connection with the bound states in continuum phenomenon is highlighted.