To improve corporate performance, it is necessary to actively inspire the service mindset and customer-oriented thinking of employees—who are internal customers—through a marketing approach. This gives rise to the need for internal marketing, which regards internal employees as customers and manages them systematically and strategically as such. Accordingly, this study aims to introduce the concept and definition of internal marketing and to empirically demonstrate the effects of applying theories and strategies developed in consumer marketing to employees. To achieve this objective, the study focused on segmenting employees of domestic advertising agencies according to appropriate criteria and differentiating the compensation packages offered to each segment, thereby enhancing the overall utility that employees derive from compensation. The research findings revealed that education and training emerged as the most important compensation factor, and that the preference variable for compensation factors was identified as the optimal variable for segmenting employees. Moreover, segmentation based on this variable increased employees' utility from compensation packages by approximately 23%.