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We investigate the surface plasmon resonance at the interface between air and n-type (100) oriented-InAs as an active material with a time-domain attenuated total reflection technique with coherent terahertz pulses. The characteristic spectra of the attenuated total reflectivity and phase shift caused by surface plasmon are observed in the Otto configuration. The surface plasmon resonance frequency and the phase jump strongly depend on the wave vector of the evanescent wave, the refractive index of the prism, and the incident angle of the terahertz pulses and the distance between the prism and active material. These features can no longer be explained with conventional Otto's approximation. We show that the interference effect between the electromagnetic wave reflected at the prism-air interface and that reemitted from excited surface plasmon plays a key role in the surface plasmon resonance.