According to F. A. Hayek, in the Field of Patents, Copyright, and Trade-Marks, a Slavish Application of the Concept of Property Has Greatly Fostered the Growth of Monopoly

Although defenders of patents often try to deny that patents constitute monopoly privileges by arguing that the term “monopoly” is inapplicable, such an argument is merely semantic. There is no contradiction or incompatibility between the notions of “patent as property” and “patent as monopoly,” and, in practice, they are closely related, since the monopolistic nature of patents is precisely what confers economic value upon them. According to Sigmund Timberg:

A patent serves a fourfold purpose. Viewed morally and socially, and perhaps psychologically, it is a reward for unusual inventive ability. From the standpoint of economics and commercial law, it is a property right. Neither of these purposes—the reward to the inventor or the creation of a property right—have any restrictive economic effect in and of themselves. But then we come to the patent’s third phase—from the vantage point of the state, a patent is a grant of a monopoly to the inventor based on the public interest in promoting the growth and diffusion of technology. It is the monopoly grant that makes tangible the inventor’s reward and converts a formal into a realistic property right. Moreover, the monopoly grant has a prima facie impact on trade, because the monopoly conferred by the patent is the right to exclude others from manufacturing or selling the patented product, or from practicing the patented process.

Hayek argues:

The problem of the prevention of monopoly and the preservation of competition is raised much more acutely in certain other fields to which the concept of property has been extended only in recent times. I am thinking here of the extension of the concept of property to such rights and privileges as patents for inventions, copyright, trade-marks, and the like. It seems to me beyond doubt that in these fields, a slavish application of the concept of property as it has been developed for material things has done a great deal to foster the growth of monopoly, and that here drastic reforms may be required if competition is to be made to work. 

--Julio H. Cole, "Patents and Copyrights: Do the Benefits Exceed the Costs?" Journal of Libertarian Studies 15, no. 4 (Fall 2001): 81-82.