We report resistivity, Hall coefficient, and Seebeck coefficient measurements on a very lightly doped (1/${\mathit{R}}_{\mathit{H}}$e=7.0\ifmmode\times\else\texttimes\fi{}${10}^{16}$ holes/${\mathrm{cm}}^{3}$) single crystal of ${\mathrm{CoSb}}_{3}$. The low-temperature resistivity is semiconducting, with a gap ${\mathit{E}}_{\mathit{g}}$=580 K (\ensuremath{\approxeq}50 meV). At high temperatures another energy scale is apparent, with a characteristic energy ${\mathit{E}}_{\mathit{g}}$=3650 K (\ensuremath{\approxeq}0.31 eV). The presence of two energies is consistent with a recent band-structure calculation performed by Singh and Pickett. The Hall coefficient is large and positive, as expected for a lightly doped p-type semiconductor. Below 200 K, the Hall mobility ${\mathit{R}}_{\mathit{H}}$\ensuremath{\sigma} varies as ${\mathit{T}}^{3/2}$, indicating that ionized impurity scattering is the dominant scattering mechanism. The Hall mobility peaks at 250 K at a value of 1940 ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$. The Seebeck coefficient is small at low temperature, and increases smoothly until it attains a value of 225 \ensuremath{\mu}V/K at 300 K; its temperature dependence is also consistent with ionized impurity scattering. A detailed structural refinement on our crystals gives a lattice parameter of 9.035 73(3) \AA{}, with evidence for little or no site disorder.