Flat gas burner (1; 101) for a cooking hob (2; 102) of the type comprising: a. a burner cup (3; 103) provided with at least one ejection nozzle (4; 104) of the fuel gas, and provided with means for the connection to said cooking hob (2; 102); b. at least one mixer (7; 107) of the fuel gas with primary air placed downstream of said at least one ejector nozzle (4; 104) and fed with fuel gas from said at least one nozzle (4; 104); c. a burner body (6.1, 6.2; 106) removably coupled to the cup (3; 103) of the burner and comprising at least part of a distribution chamber (8; 108) of the mixture composed of fuel gas/primary air placed downstream of said at least one mixer (7; 107); and d. at least one flame spreader (9; 109), comprising at least one horizontal surface or zones tilted of few degrees with respect to the horizontal line, coupled to said at least one distribution chamber (8; 108) and provided with flame holes (18; 118) having respective outflow sections of the mixture composed of fuel gas/primary air which substantially lie on said at least one horizontal surface or zones tilted of few degrees with respect to the horizontal line on one or more planes inclined of an angle comprised in the range 0° - 30° with respect to the horizontal line and configured to produce a plurality of flames departing substantially vertically from the flame spreader, said at least one flame spreader (9; 109) having a central opening (10; 110) for the outflow of the secondary air; wherein said burner body (6.1, 6.2; 106) comprises at least part of the structure of at least one inflow ductwork (16.1, 16.2; 116) of secondary air towards said central opening (10; 110) for the outflow of the secondary air; said at least one inflow ductwork (16.1, 16.2; 116) of secondary air having a drawing section (17.1, 17.2; 117) to draw secondary air configured to open over said cooking hob (2; 102); wherein it comprises at least one inflow ductwork (12.1, 12.2; 112) of primary air fluidically connected to said at least one mixer (7; 107), said at least one inflow ductwork (12.1, 12.2; 112) of primary air having its own drawing section (13.1, 13.2; 113) configured to draw primary air over the cooking hob (2; 102). a. a burner cup (3; 103) provided with at least one ejection nozzle (4; 104) of the fuel gas, and provided with means for the connection to said cooking hob (2; 102); b. at least one mixer (7; 107) of the fuel gas with primary air placed downstream of said at least one ejector nozzle (4; 104) and fed with fuel gas from said at least one nozzle (4; 104); c. a burner body (6.1, 6.2; 106) removably coupled to the cup (3; 103) of the burner and comprising at least part of a distribution chamber (8; 108) of the mixture composed of fuel gas/primary air placed downstream of said at least one mixer (7; 107); and d. at least one flame spreader (9; 109), comprising at least one horizontal surface or zones tilted of few degrees with respect to the horizontal line, coupled to said at least one distribution chamber (8; 108) and provided with flame holes (18; 118) having respective outflow sections of the mixture composed of fuel gas/primary air which substantially lie on said at least one horizontal surface or zones tilted of few degrees with respect to the horizontal line on one or more planes inclined of an angle comprised in the range 0° - 30° with respect to the horizontal line and configured to produce a plurality of flames departing substantially vertically from the flame spreader, said at least one flame spreader (9; 109) having a central opening (10; 110) for the outflow of the secondary air;