The study introduces a parsimonious semiparametric class-specific index regression that captures heterogeneous covariate--response relationships across latent subpopulations. In such a latent class model formulation, subject-specific indices are used as a complete-data representation of the realized latent labels. We propose a unified framework for estimating model parameters and recovering latent class memberships. For the class-specific index mean model, estimation and latent class recovery are conducted via a pseudo-least-squares criterion with a separation penalty, and a semiparametric information criterion is proposed for consistently estimating the number of classes. Exploiting the response distribution, we develop a Bayes classification rule that maximizes the asymptotic probability of correct assignment and a pseudo-maximum likelihood criterion that yields class index coefficient estimators with asymptotic semiparametric efficiency. This refinement step characterizes latent class membership probabilities via sufficient dimension reduction of the covariate space. Simulations and applications to marketing and biomedical datasets demonstrate superior finite-sample performance of the proposed methodology in parameter estimation, latent class recovery, and class number selection.

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