[I'm a US resident so this may be culturally irrelevant for France.] Working harder is not really the answer. I never found it useful to bust my hump to get a

[I'm a US resident so this may be culturally irrelevant for France.] Working harder is not really the answer. I never found it useful to bust my hump to get a 5% raise when I could just go to another company for a 10-15% raise. I loved my work and the companies I worked for but business is business. If they got you cheap initially, they will almost never reevaluate you and pay you a market rate. 5 years at the same company is forever in the developer biz.