An approach to time-domain terahertz reflection spectroscopy is proposed and demonstrated. It allows one to obtain very accurately the relative phase of a reflected THz wave form, and consequently the complex dielectric function can be precisely extracted. The relevant setup was demonstrated to allow measurements of a variety of samples: we present results for doped silicon and for ferroelectric SrBi 2 Ta 2 O 9 bulk ceramics as well as thin film on sapphire substrates. © 2003 American Institute of Physics.