This work presents the finite-time blow-up of solutions to the equation u(tt) - Delta u = a(-k) vertical bar u vertical bar(p), in the Minkowski space. We extend the previous result of Belchev, Kepka and Zhou [E. Belchev, M. Kepka, Z. Zhou, Finite-time blow-up of solutions to semilinear wave equations, J. Funct. Anal. 190 (1) (2002) 233-254] comprehensively. Due to a modification of the so-called method of conformal compactification used by Belchev, Kepka and Zhou, we show that the solutions blow up in finite time with more relaxed initial data and extended index p. (c) 2007 Elsevier Ltd. All rights reserved.