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This paper presents an investigation on nonlinear propagation of quadruple Gaussian (Q.G) laser beam in narrowband semiconductor (e.g., n-type InSb) plasmas. In the presence of laser beam, the electron fluid in the conduction band becomes relativistic that makes the medium highly nonlinear. As a result the laser beam gets self-focused. Following variational theory approach in W.K.B approximation the numerical solution of the nonlinear Schrodinger wave equation (NSWE) for the field of incident laser beam has been obtained. Particular emphasis is put on dynamical variations of beam spot size and longitudinal phase (Gouy phase). Self-trapping of the laser beam resulting from the dynamical balance between diffraction broadening and nonlinear refraction also has been investigated.