AFAIK there is no legal minimum wage.
Wikipedia in German states (here follows a rough, summed up translation) that a minimum wage of CHF 3550.00 is recommended. Branches, such as gastronomy and retail tend to employ staff for lower wages - between CHF 2700.00 and CHF 3300.00. Wages under CHF 3000.00 are frowned upon (rightly so, in my opinion) and there are endeavours to introduce a legal minimum wage of CHF 3000.00