We consider the problem of determining the presence of genuine multipartite entanglement through the violation of Mermin's Bell-type inequality (MI). Though the violation of MI cannot certify the presence of genuine nonlocality, but can certify genuine tripartite entanglement whenever the violation is strictly greater than 2 √ 2. Here we show that MI suffices as genuine entanglement witness even when its value is 2 √ 2 if at least two of the local marginal distributions are not completely random provided the local Hilbert space dimension of at least one of the sub-systems is two. Thus local marginals suffice as semi-device independent genuine entanglement witness. This is intriguing in a sense, as the local properties of a composite system can help to identify its global property. Furthermore, analyzing another quantity constructed from Mermin polynomials we show that genuine entanglement certification task for the correlations with MI violation equal to 2 √ 2 can actually be made fully device independent.PACS numbers: 03.65. Ud, 03.67.Mn Entanglement is considered to be one of the most bizarre nonclassical manifestations of multipartite quantum systems. Linearity of quantum mechanics (QM) allows to build superposed states that cannot be written as product of states of each subsystems and hence resulting in entangled states. Entanglement lies at the core of some of the most puzzling features of QM: the Einstein-Podolski-Rosen (EPR) argument [1], the Schrodinger's steering concept [2], and most importantly the nonlocal behaviour of QM [3]. In the past three decades quantum entanglement has also been established as a useful resource for several information theoretic tasks: quantum cryptography [4], quantum teleportation [5], quantum superdense coding [6] are few noteworthy among many others.While the state of a quantum system composed of only two subsystems can be either separable or entangled, for a quantum system with more than two subsystems the separability properties have a complicated structure. In the multipartite scenario the most dramatic attribute appearing in the picture is the concept of truly or genuinely multipartite entanglement (GME) which cannot be prepared by mixing states that are separable with respect to some partition [7][8][9][10]. Whereas Greenberger, Horne, and Zeilinger established implication of GME in quantum foundations by reveling perfect incompatibility of QM with EPR idea of local deterministic world view [7], significant advantages of it compared to bipartite entanglement has also been established in different practical tasks, namely, extreme spin squeezing [11], high sensitivity in some general metrology tasks [12], quantum computing using cluster states [13], measurement-based quantum computation [14], various quantum communication protocols [15], secret sharing among multiple parties and multiparty quantum network [16]. Despite its importance, characterization and detection of entanglement is quite difficult. Several methods such as tomography of the full state [17], construc...