NOVELTY - The device comprises an etching vessel (5) for an etching liquid (22); a reservoir (7) for the etching liquid connected to the etching vessel by a fluid line (50, 52, 54, 56, 58); a circulating pump (9)connected/designed to the etching vessel and the reservoir; a fluid circuit from the etching vessel, via the reservoir, and the fluid line back to the etching vessel; and a detection device connected to the fluid circuit. The detection device is designed to detect a concentration such as a consumption of a component of the etching fluid.    USE - The device is useful for etching semiconductor wafers such as silicon wafers for solar cells.    ADVANTAGE - The device is capable of rapidly and economically etching semiconductor wafers with high quality.    DETAILED DESCRIPTION - The device comprises an etching vessel (5) for an etching liquid (22); a reservoir (7) for the etching liquid connected to the etching vessel by a fluid line (50, 52, 54, 56, 58); a circulating pump (9)connected/designed to the etching vessel and the reservoir; a fluid circuit from the etching vessel, via the reservoir, and the fluid line back to the etching vessel; and a detection device connected to the fluid circuit. The detection device is designed to detect a concentration such as a consumption of a component of the etching fluid, and to produce a concentration signal representing the concentration and emit same on the output side. The detection device comprises: an acoustic sensor; a conductivity sensor; a surface tension sensor; and a processing unit. The acoustic sensor is formed to generate the concentration of the component as a function of the detection parameter namely a sound propagation velocity of sound in the etching liquid and to generate a corresponding sound-speed signal as an output signal. The conductivity sensor is formed to detect the detection parameters namely an electrical conductivity of the etching liquid and to generate a corresponding conductivity signal as the output signal. The surface tension sensor is formed to detect the detection parameter namely a surface tension of the etching liquid and to generate a corresponding surface tension signal as the output signal. The detection device is formed to produce the concentration signal as a function of the surface tension signal and the conductivity signal. The processing unit is formed to detect and store the detection parameter representing the output signal of a map data set that represents the detection parameter as a function of the concentration of the component. The processing unit is formed to produce in dependence of the output signal of the concentration signal by map data set. The map data set is formed by a multi-dimensional polynomial and a neural network. An INDEPENDENT CLAIM is included for a method for etching semiconductor wafers such as silicon wafers for solar cells.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a device for etching semiconductor wafers.    Etching vessel (5)    Reservoir (7)    Circulating pump (9)    Etching liquid (22)    Fluid line. (50, 52, 54, 56, 58)