Summary: We study semilinear wave equations with Ginzburg-Landau-type nonlinearities, multiplied by a factor of \(\epsilon^{-2}\), where \(\epsilon>0\) is a small parameter. We prove that for suitable initial data, the solutions exhibit energy-concentration sets that evolve approximately via the equation for timelike Minkowski minimal surfaces, as long as the minimal surface remains smooth. This gives a proof of the predictions made (on the basis of formal asymptotics and other heuristic arguments) by cosmologists studying cosmic strings and domain walls, as well as by applied mathematicians.