This paper concerns the study of the numerical approximation for the following initialboundary value problem \documentclass[12pt]{minimal}
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\left\{ \begin{gathered}
u_t - u_{xx} = f\left( u \right), x \in \left( {0,1} \right), t \in \left( {0,T} \right), \hfill \\
u\left( {0,t} \right) = 0, u_x \left( {1,t} \right) = 0, t \in \left( {0,T} \right), \hfill \\
u\left( {x,0} \right) = u_0 \left( x \right), x \in \left[ {0,1} \right], \hfill \\
\end{gathered} \right.
$$\end{document} where f(s) is a positive, increasing, C1 convex function for the nonnegative values of s, f(0) > 0, \documentclass[12pt]{minimal}
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\frac{{ds}}
{{f\left( s \right)}}
$$\end{document} < ∞, u0 ∈ C1([0, 1]), u0(0) = 0, u′0(1) = 0. We find some conditions under which the solution of a semidiscrete form of the above problem blows up in a finite time and estimate its semidiscrete blow-up time. We also prove the convergence of the semidiscrete blow-up time to the theoretical one. A similar study has been also undertaken for a discrete form of the above problem. Finally, we give some numerical results to illustrate our analysis.