<p style='text-indent:20px;'>This paper is devoted to investigating formation of singularities for solutions to semilinear Moore-Gibson-Thompson equations with power type nonlinearity <inline-formula><tex-math id="M1">\begin{document}$ |u|^{p} $\end{document}</tex-math></inline-formula>, derivative type nonlinearity <inline-formula><tex-math id="M2">\begin{document}$ |u_{t}|^{p} $\end{document}</tex-math></inline-formula> and combined type nonlinearities <inline-formula><tex-math id="M3">\begin{document}$ |u_{t}|^{p}+|u|^{q} $\end{document}</tex-math></inline-formula> in the case of single equation, combined type nonlinearities <inline-formula><tex-math id="M4">\begin{document}$ |v_{t}|^{p_{1}}+|v|^{q_{1}} $\end{document}</tex-math></inline-formula>, <inline-formula><tex-math id="M5">\begin{document}$ |u_{t}|^{p_{2}}+|u|^{q_{2}} $\end{document}</tex-math></inline-formula>, combined and power type nonlinearities <inline-formula><tex-math id="M6">\begin{document}$ |v_{t}|^{p_{1}}+|v|^{q_{1}} $\end{document}</tex-math></inline-formula>, <inline-formula><tex-math id="M7">\begin{document}$ |u|^{q_{2}} $\end{document}</tex-math></inline-formula>, combined and derivative type nonlinearities <inline-formula><tex-math id="M8">\begin{document}$ |v_{t}|^{p_{1}}+|v|^{q_{1}} $\end{document}</tex-math></inline-formula>, <inline-formula><tex-math id="M9">\begin{document}$ |u_{t}|^{p_{2}} $\end{document}</tex-math></inline-formula> in the case of coupled system, respectively. More precisely, blow-up results of solutions to problems in the sub-critical and critical cases are derived by applying test function technique. Moreover, upper bound lifespan estimates of solutions to the coupled systems are investigated. The main new contribution is that lifespan estimates of solutions are associated with the well-known Strauss exponent and Glassey exponent.</p>