MultiJunction Solar Cells (MJSC) offer the possibility to overcome the maximum theoretical efficiency limit of single junction solar cells by associating several PN junctions (or subcells) in one device. In order to develop ever more efficient devices, it is important to detect the presence of defects causing intermediate energy levels in the gap of the materials and degrading the performance. Admittance Spectroscopy (AS) and Deep-Level Transient Spectroscopy (DLTS) are two powerful techniques widely use to characterize defects in single junction solar cells [1,2]. In the literature, there are almost no studies using these techniques for the characterization of defects in MJSC. Indeed, among all the existing MJSC configurations, the most developed associate the subcells in series (2 terminal -2T configuration). Therefore, due to the electrical and optical coupling between the junctions in those structures, it is difficult to separate and exploit the contribution of each subcell. In recent work, we have detailed a simple and non-destructive method to separate the admittance contribution of each subcell in a 2T Tandem Solar Cell (TSC) [3]. It has been shown that under a specific illumination where only one of the subcells fully absorbs the light, the capacitance of the absorbing cell can be shunted, so that the measured capacitance of the TSC becomes representative of the non-absorbing subcell only. We propose here to extend this method for the characterization of MJSC using AS and DLTS techniques. Based on numerical modelling and theoretical developments we show how it is possible to extract the defect parameters in each subcell of a TSC by combining the use of light biases with AS or DLTS. For example: Fig. 1 illustrates the DLTS spectra of: (a) an AlGaAs single junction modelled with a defect D1; (b) a TSC built with the previous cell as the top subcell and a Si cell as the bottom subcell with a defect D2; (c) the TSC structure illuminated with a light bias absorbed only by the bottom subcell. DLTS spectra of the TSC in the dark don’t show any signature of the defect D1. Only the defect D2 is visible with a parasitic phenomenon (labelled D3). Once the bottom cell absorbs the light, one can clearly see the signature of the defect in the top subcell only. The method based on AS and DLTS proposed here to probe defect states can be generalized to any kind of multijunction solar cell, using appropriate light biases. [1] D.L. Losee, Admittance spectroscopy of impurity levels in Schottky barriers, J. Appl. Phys. 46 (1975) 2204. https://doi.org/10.1063/1.321865. [2] D. V. Lang, Deep‐level transient spectroscopy: A new method to characterize traps in semiconductors, J. Appl. Phys. 45 (1974) 3023. https://doi.org/10.1063/1.1663719. [3] C. Leon, S. Le Gall, M.-E. Gueunier-Farret, A. Brézard-Oudot, A. Jaffre, N. Moron, L. Vauche, K. Medjoubi, E.V. Vidal, C. Longeaud, J.-P. Kleider, Understanding and monitoring the capacitance-voltage technique for the characterization of tandem solar cells, Prog. Photovoltaics Res. Appl. 28 (2020) 601–608. https://doi.org/10.1002/PIP.3235.