A study of the identification properties and of the energy response of a Si-Si-CsI(Tl) E-E telescope exploiting a partially depleted second Si stage has been performed. Five different bias voltages have been applied to the second stage of the telescope, one corresponding to full depletion, the others associated with a depleted layer ranging from 60% to 90% of the detector thickness. Fragment identification has been obtained using either the E-E technique or the Pulse Shape Analysis (PSA). Charge collection efficiency has been evaluated. The E-E performance is not affected by incomplete depletion. Isotopic separation capability improves at lower bias voltages with respect to full depletion, though charge identification thresholds increase.