In this report, we present the measurements of open charm production at mid-rapidity in p+p, d+Au, and Au+Au collisions at RHIC energies. The techniques of direct reconstruction of open charm via its hadronic decay and indirect measurements via its semileptonic decay are discussed. The beam energy dependence of total charm cross section, electron p_T spectra, and their comparisons to theoretical calculations, including NLO pQCD, are presented. The electron spectra in p+p, d+Au, and Au+Au collisions at sqrt S_{NN}=200 GeV show significant variation. The open charm absolute cross section at midrapidity and its centrality dependence are compared to those of inclusive hadrons integrated over p_T>1.5 GeV/c.

PACS numbers: 25.27.Dw, 13.20.Fc, 13.25.Ft