We investigate the phase diagram and finite-temperature transitions of three-dimensional scalar SO(Nc) gauge theories with N f ≥ 2 scalar flavors. These models are constructed starting from a maximally O(N )-symmetric multicomponent scalar model (N = NcN f ), whose symmetry is partially gauged to obtain an SO(Nc) gauge theory, with O(N f ) or U(N f ) global symmetry for Nc ≥ 3 or Nc = 2, respectively. These systems undergo finite-temperature transitions, where the global symmetry is broken. Their nature is discussed using the Landau-Ginzburg-Wilson (LGW) approach, based on a gauge-invariant order parameter, and the continuum scalar SO(Nc) gauge theory. The LGW approach predicts that the transition is of first order for N f ≥ 3. For N f = 2 the transition is predicted to be continuous: it belongs to the O(3) vector universality class for Nc = 2 and to the XY universality class for any Nc ≥ 3. We perform numerical simulations for Nc = 3 and N f = 2, 3. The numerical results are in agreement with the LGW predictions.