We report measurements of the charge-separated W +(−) → e +(−) + νe(νe) and Z/γ * → e + e − production cross sections at mid-rapidity in proton-proton collisions at √ s = 500 GeV. These results are based on 13.2 pb −1 of data recorded in 2009 by the STAR detector at RHIC. Production cross sections for W bosons that decay via the eν channel were measured to be σ(pp → W + X)·BR(W + → e + νe) = 117.3 ± 5.9(stat) ± 6.2(syst) ± 15.2(lumi) pb, and σ(pp → W − X)·BR(W − → e −ν e) = 43.3 ± 4.6(stat) ± 3.4(syst) ± 5.6(lumi) pb. For Z/γ * production, σ(pp → Z/γ * X)·BR(Z/γ * → e + e − ) = 7.7 ± 2.1(stat) +0.5 −0.9 (syst) ± 1.0(lumi) pb was measured for di-lepton invariant masses m e + e − between 70 and 110 GeV/c 2 . First measurements of the W cross section ratio, σ(pp → W + X)/σ(pp → W − X), at √ s = 500 GeV are also reported. Theoretical predictions, calculated using recent parton distribution functions, are found to agree with the measured cross sections.