We construct and study a time-semidiscretization scheme for the Cauchy problem associated with a linear homogeneous differential equation with the Caputo fractional time derivative of order α ∈ (0, 1) and a spatial sectorial operator in a Banach space. For this scheme, we obtain rate-of-convergence and error estimates in terms of the discretization step. We use properties of Mittag-Leffler functions, hypergeometric functions, and the calculus of sectorial operators in a Banach space. Results of numerical experiments are also reported.