Fiber matrix semifinished product containing i) at least one fibrous material selected from the group consisting of scrims, woven fabrics, braids, knitted fabrics, nonwovens, rovings, mats, knitted fabrics and combinations thereof, of glass fibers, carbon fibers, mineral fibers, natural fibers, synthetic fibers, and/or combinations thereof; and ii) a thermoplastic matrix, characterized in that the latter comprises A) 10 to 97% by weight, of at least one thermoplastic from the group of polycarbonates, and B) from 3 to 90% by weight of one or more phosphazenes of the formula and/or one or more phosphazenes corresponding to formula in which R 1, R 2 are identical or different and represent an alkyl, cycloalkyl, aryl or alkylaryl, R 3, R 4 are identical or different and represent alkyl, cycloalkyl, aryl or alkylaryl, R 5 represents -N=P(OR 3) 3, -N=P(OR 4) 3, -N=P OR 3 or -N=P OR 4, R 6 is -N=P(OR 3) 4, -N=P(OR 4) 4, -N=P (OR 3) 2 or -N=P (OR 4) 2, a is an integer in the range from 3 to 25, and b is an integer in the range from 3 to 1000, wherein the sum of the percentages by weight in the thermoplastic matrix ii) is always 100 and wherein the fibrous material i) is impregnated with the thermoplastic matrix ii) and the volume fraction of the fibrous material i) in the fibrous matrix semifinished product is in the range from 25 to 65% by volume and, in addition to the components A) and B), component C) comprising 0.001 to 2% by weight of at least of a thermostabilizer selected from the group of aliphatically substituted phosphites is used, wherein at least one of components A) or B) is to be varied within the specified quantitative ranges in such a way that the sum of all the percentages by weight of components A), B) and C) based on the thermoplastic matrix ii) is always 100, the molecular weight of the thermostatic stabilizer to be used as component C) is greater than 650 g/mol. i) at least one fibrous material selected from the group consisting of scrims, woven fabrics, braids, knitted fabrics, nonwovens, rovings, mats, knitted fabrics and combinations thereof, of glass fibers, carbon fibers, mineral fibers, natural fibers, synthetic fibers, and/or combinations thereof; and ii) a thermoplastic matrix, characterized in that the latter comprises A) 10 to 97% by weight, of at least one thermoplastic from the group of polycarbonates, and B) from 3 to 90% by weight of one or more phosphazenes of the formula and/or one or more phosphazenes corresponding to formula in which R 1, R 2 are identical or different and represent an alkyl, cycloalkyl, aryl or alkylaryl, R 3, R 4 are identical or different and represent alkyl, cycloalkyl, aryl or alkylaryl, R 5 represents -N=P(OR 3) 3, -N=P(OR 4) 3, -N=P OR 3 or -N=P OR 4, R 6 is -N=P(OR 3) 4, -N=P(OR 4) 4, -N=P (OR 3) 2 or -N=P (OR 4) 2, a is an integer in the range from 3 to 25, and b is an integer in the range from 3 to 1000, wherein the sum of the percentages by weight in the thermoplastic matrix ii) is always 100 and wherein the fibrous material i) is impregnated with the thermoplastic matrix ii) and the volume fraction of the fibrous material i) in the fibrous matrix semifinished product is in the range from 25 to 65% by volume and, in addition to the components A) and B), component C) comprising 0.001 to 2% by weight of at least of a thermostabilizer selected from the group of aliphatically substituted phosphites is used, wherein at least one of components A) or B) is to be varied within the specified quantitative ranges in such a way that the sum of all the percentages by weight of components A), B) and C) based on the thermoplastic matrix ii) is always 100, the molecular weight of the thermostatic stabilizer to be used as component C) is greater than 650 g/mol. A) 10 to 97% by weight, of at least one thermoplastic from the group of polycarbonates, and B) from 3 to 90% by weight of one or more phosphazenes of the formula and/or one or more phosphazenes corresponding to formula in which R 1, R 2 are identical or different and represent an alkyl, cycloalkyl, aryl or alkylaryl, R 3, R 4 are identical or different and represent alkyl, cycloalkyl, aryl or alkylaryl, R 5 represents -N=P(OR 3) 3, -N=P(OR 4) 3, -N=P OR 3 or -N=P OR 4, R 6 is -N=P(OR 3) 4, -N=P(OR 4) 4, -N=P (OR 3) 2 or -N=P (OR 4) 2, a is an integer in the range from 3 to 25, and b is an integer in the range from 3 to 1000, R 1, R 2 are identical or different and represent an alkyl, cycloalkyl, aryl or alkylaryl, R 3, R 4 are identical or different and represent alkyl, cycloalkyl, aryl or alkylaryl, R 5 represents -N=P(OR 3) 3, -N=P(OR 4) 3, -N=P OR 3 or -N=P OR 4, R 6 is -N=P(OR 3) 4, -N=P(OR 4) 4, -N=P (OR 3) 2 or -N=P (OR 4) 2, a is an integer in the range from 3 to 25, and b is an integer in the range from 3 to 1000,