A one-piece silicon device with flexible blades (2, 3), in particular for timepieces, for example a pivot with crossed blades, and to a method for manufacturing the device (1). The method includes: forming (21) a one-piece silicon device (1) blank from a wafer of the SOI type, the device (1) including two flexible blades (2, 3), each formed in a different layer of the SOI wafer, the blades (2, 3) being arranged in two different substantially parallel planes, the blades (2, 3) being separated by a clearance (7); growing a first silicon oxide layer on the surface of at least one of the blades (2, 3) bordering the clearance, the first silicon oxide layer being formed from a first sub-layer of silicon of the one or more blades (2, 3); and removing the first silicon oxide layer to increase the clearance (7) between the two blades (2, 3).