We report the observation of focusing of low energy electrons by submicrometer pits patterned onto a silicon crystal surface. Images of an array of pits obtained with a low energy electron microscope consist of an array of bright spots whose diameters depend strongly on the energy of the incident electrons. Our electron-optical simulation shows that each pit acts like an electrostatic lens, focusing the electrons along its optical axis, with a focal position which indeed depends strongly on the incident energy.