A series of pyrite thin films were deposited in-situ in a monolayer-by-monolayer fashion using sequential evaporation of iron under high vacuum, followed by sulfidation at a sulfur pressure of 133 Pa, as a function of substrate temperature. The stoichiometry, crystallinity, topographic smoothness, and phase purity of the deposited pyrite thin films improve with increasing substrate temperature up to 420 degrees C, the highest temperature studied. Characterization of the films deposited at 420 degrees C using selected-area precession electron diffraction, Raman Spectroscopy, and conventional X-ray diffraction indicated that the pyrite layer is phase pure, with no evidence of a secondary marcasite phase, and grew in columnar grains with a preferential (100) orientation on the (100) silicon substrates. This novel sequential evaporation technique has the potential to make useful low-cost semiconducting pyrite materials for large-area electronic applications.