Epitaxial barium titanate (BTO) thin films are grown on strontium titanate-buffered Si(001) using atomic layer deposition (ALD) at 225 °C. X-ray diffraction confirms compressive strain in BTO films after the low temperature growth for films as thick as 66 nm, with the BTO c-axis oriented in the out-of-plane direction. Postdeposition annealing above 650 °C leads to an in-plane c-axis orientation. Piezoresponse force microscopy was used to verify the ferroelectric switching behavior of ALD-grown films. Electrical and electro-optic measurements confirm BTO film ferroelectric behavior in out-of-plane and in-plane directions, respectively, at the micrometer scale.