Product semantics,the ''study of the symbolic qualities of man-made forms in the context of their use and application of this knowledge to industrial design'' is an important challenge in product design. Because of subjectivity, this particular dimension of the user's need is difficult to express,to quantify and to assess. This paper presents a general approach to assess product semantics in a sound way. It is based on usability tests,and involves several classical methods in marketing and decision-making theory,as multidimensional scaling,semantic differential method,factor analysis,pairwise comparison and analytical hierarchy process. As a result, our integrated approach provides designers with a tool which helps understand and specify the semantic part of the need; it rates and ranks the new product prototypes according to their closeness to the specified ''ideal product'',and it underlines the particular semantic dimensions that should be improved. To illustrate our approach,we have performed usability tests and applied our methodology to the design of table glasses. For the sake of clarity,each stage of the methodology is presented in detail on this particular example.