The physisorption of cyclohexane vapor onto silicon wafers with grossly different oxide layer thicknesses delta (25 and 570 nm) was studied in the temperature range 15-40 degrees C by ellipsometry. Isotherms of film thickness d exhibit an extended linear region up to a relative pressure p/p(0) approximate to 0.7, with a small and nearly temperature independent slope partial derivative d/partial derivative(p/p(0)), indicating weak adsorbate-substrate interactions. Above p/p(0) = 0.7 the isotherms show a pronounced temperature dependence and reveal a wetting transition with a wetting temperature T-w near 20 degrees C, i.e., ca. 14 K above the triple point of the adsorptive. Above T-w the film thickness increases steeply, with values exceeding 20 nm near the saturation pressure p(0), as expected for complete wetting. Below T-w the film thickness reaches only a few monolayers at p(0). In the temperature range just above T-w a pronounced hysteresis is observed in pressure quenches near saturation, which is explained by temperature excursions on crossing the prewetting line. The multilayer regime of the-isotherms above T-w was analyzed in terms of the Frenkel-Halsey-Hill (FHH) equation, ln(p/p(0)) = -(alpha/kT)d(-n), where the exponent n is expected to have a value of 3 for nonretarded dispersion force interactions and for sufficiently large d. The present data for the range from above one monolayer up to p/p(0) = 0.95 yield much lower values (n = 1.65 +/- 0.2 and 1.0 +/- 0.2 for wafers with delta = 25 nm and 570 nm, respectively). These low values of n are consistent with results of theoretical physisorption isotherms obtained by the Born-Green-Yvon theory when the interaction parameters are chosen in a way to reproduce the observed wetting transition. From these results it is concluded that the low values of n found in this study are characteristic for wetting systems just above the wetting transition.