This paper introduces a new technique to determine the optimum horizontal-well completion design in terms of the optimum horizontal-well length, the minimum wellbore/reservoir pressure drop, and the maximum wellbore/reservoir productivity index (PI) at pseudo-steady state (PSS). Frictional-wellbore pressure losses (FWPL) are accounted for based on a new general semi-analytical PSS finite-conductivity model (FCM) for a horizontal well under a rectangular bounded reservoir producing at a constant rate. The PSS FCM is coupling a PSS infinite-conductivity model (ICM) with a frictional-wellbore model (FWM) by using their correct-discretization resolution of the wellbore (CDRW), which has never been achieved before. The new FWM is developed in a general form to be coupled easily with any general ICM and can be applied at any time of the well production life. Two field examples are presented to show the effect of different reservoir, well, and fluid properties on horizontal-well performance.The new technique is based on the optimization of dimensionless well length (LD) between the two systems (i.e., ICM and FWM) of the FCM because LD is directly proportional to the PI of the first system and inversely proportional to the PI of the second system. Therefore, there is always a minimum point on the wellbore/reservoir pressure drop curve corresponds to a maximum point on the wellbore/reservoir PI curve.Results show that: 1. LD has the key role in the wellbore/reservoir coupling model.2. FWPL is crucial if both well production rate (qw) and horizontal permeability (kh) are high, where a notable drop in FCM PSS PI occurs, recommending shortening to the horizontal-well length.3. FWPL is insignificant if qw is low and oil viscosity (μo) is high, where no decrease in FCM PSS PI occurs, recommending lengthening to the horizontal-well length.4. Wellbore segment length (ΔL) of the FWM must be small, ΔL = 0.25 ft in this study. If it is not enough small, a critical overestimation may be occurred in the optimum horizontal-well length and the maximum PSS PI of the horizontal-well completion design.